With the increasing demands for communications, high-speed transport systems have been standardized. For example, ITU-T (International Telecommunication Union Telecommunication Standardization Sector) G.709 standard defines a technology of optical transport network (OTN) of approximately 1.25˜100 Gbps.
In optical transmissions in OTN are implemented by mapping a plurality of client signals into an optical signal having a format called OTU (Optical channel Transport Unit), and a large capacity of transmission is thus realized. Examples of the client signals mapped into the OTU frame are the SDH (Synchronous Digital Hierarchy) frame, SONET (Synchronous Optical NET) frame, and Ethernet (registered trademark) frame. Therefore, the OTN technology is expected as a transport means having a large capacity in core networks.
When data of the client signals are multiplexed by TDM (Time Division Multiplexing) such as OTN, the data are mapped into the payload field of a time division multiplexing signal by GFP (Generic Framing Procedure), for example. As GFP, there are frame mapped GFP-F and transparent mapped GFP-T.
GFP-F performs mapping of data of the client signal for each packet or frame that forms the client signal. GFP-T performs mapping of data of the client signal by bit sampling independently of packet or frame boundaries. Thus, GFP-T enables transparent transmission of the client signal. The technologies of GFP-F and GFP-T are defined in ITU-T Recommendation G.7041/Y.1303.
GFP-T does not need synchronization processing of packets or frames, and has hardware that is less expensive than GFP-F. Thus, GFP-T is often employed in transmission devices of access networks in which extreme cost reduction has been progressing.
As to GFP, Japanese Laid-Open Patent Publication No. 2012-165334 discloses auto-negotiation enabled in mapping of the client signal by GFP-F between client devices. Japanese Laid-Open Patent Publication No. 2011-176750 discloses mapping of client signals into the OTN frame.
Since GFP-T implements the transparent transmission, the number of communication channels and the bandwidth for transmitting and receiving the client signal are set equal to the number of theoretical communication channels (tributary slots) and the bandwidth formed in the time division multiplexing signal (for example, OTU frame). For example, if 40 1 GbE (gigabit Ethernet) signals are stored in a time division multiplexing signal, 40 tributary slots each handling the 1 GbE signal are used in the interface with the client-side network.
Thus, the 40 1 GbE signals separated from the time division multiplexing signal cannot be bundled in a tributary slot of, for example, 40 Gbps of Ethernet for transmission to the client network. Thus, in order to change the communication channels in which the time division multiplexing signal is transmitted and received, it is necessary to change the communication channels in which the client signal is transmitted and received. The above change increases the cost of change and migration of the network structure.